Process for producing and recovering organic nuclear reactor coolant-moderators



PROCESS FOR PRODUtIiNG A RECOVERENG ORGANIC NUCLEAR REACTOR COOLANT-MODERATGRS Robert 0. Bolt, San Rafael, and William W. West, El Cerrito,Califi, assignors, by mesne assignments, to the United States of Americaas represented by the United States Atomic Energy Commission No Drawing.Filed Nov. 3%, 1959, Ser. No. 856,321

3 Claims. (Cl. Zita-493.2)

The present invention relates, in general, to the production andrecovery of polyphenyl coolants from intractable polyphenyl tars orresidues and, more particularly, to the treatment of intractable,insoluble tarry residues obtained from coolants or moderators employedin nuclear reactors for conversion into useful moderatorcoolantproducts.

Varieties of aromatic hydrocarbons have been utilized or have beenproposed or investigated for use as coolants or moderators in nuclearreactors including polyphenyls, aromatic condensed ring compounds,aromatic ethers and alkylated aromatic hydrocarbons. Polyphenylhydrocarbons, especially biphenyl, the terphenyls and the quaterphenylsare suitable for such use due to superior radiolytic and pyrolyticresistance and other requisite properties as disclosed in the copendingapplication of Reppino J. Fontana et al., S.N. 599,352, filed July 23,1956, now abandoned. Ordinarily, mixtures of a fluid nature or lowmelting point solids corresponding to lower average molecular weights oreutectic mixtures are preferred. Upon long continued use in the hightemperature intense radiation environment of the reactor the organicmixtures show increases in viscosity with higher molecular weightmaterials being formed therein. Eventually, insoluble high molecularweight materials may form which ma-- terials precipitate to plug reactorpassages and create a hazard to further operation of the reactor.Accordingly, in conventional practice the mixture employed in thereactor is periodically replaced or reconditioned by separating thetarry constituents by distillation, precipitation, extraction, etc. Thetarry residues obtained in such reconditioning operations represent anexpensive loss of the coolant or moderator material and the indicatedchanges of composition of the coolant lead to greater pumping cost,lower heat transfer as well as other higher operating costs for such areactor.

Nuclear reactors employing organic moderators and coolants are wellknown in the art. A reactor employing biphenyl as a moderator isdisclosed in U.S. Patent No. 2,708,656, issued May 17, 1955, to E. Fermiet al. The use of organic liquids as coolants is also disclosed inChapter 8 of Principles of Nuclear Reactor Engineering, Glasstone, VanNostrand Co., Inc., 1955. A bibliography of publications relating tosuch reactors is presented in Selected Abstracts on the Use of OrganicMaterials as Reactor Moderator-Coolants, G. Naish and .R. W. Bowring,AERE Report inf/Bib 105. Moreover,

biphenyl-terphenyl mixtures have successfully been utilized in the OMRE(organic moderated reactor experiment). C.f. Details of OMRE Nucleonics,vol. 14, No. 5, page 22, May 1956.

The reactions which occur upon radiolytic pyrolysis of V ice andincreases of the proportion of higher polyphenyls is an undesirabletendency. This is true as well for other hydrocarbons, e.g., partiallyhydrogenated or alkylated polyphenyls.

The present invention is predicated on the discovery that catalytichydrogenolysis of difierent polyphenyls produces a marked reversion orconversion of higher molecular weight constituents of aromatic andespecially polyphenyl mixtures having undesirable characteristics intolower molecular weight mixtures of more useful and desirablecoolant-moderator types. Most unexpectedly hydrogenolysis, i.e., ringcleavage occurs with little ring hydrogenation which might have beenexpected. Thus, highly damaged reactor coolant-moderator materials maybe reconditioned or various component fractions thereof separated andtreated to provide a material which is highly satisfactory for reuse inthe reactor.

Accordingly, it is an object of the present invention to provide amethod for reconditioning coolant-moderator materials for use in anuclear reactor. I

Another object of the invention is to employ a catalytic hydrogenolysistreatment for converting higher molecular weight reactorcoolant-moderators into more desirable coolant-moderators.

Still another object of the invention is to provide a method ofconverting high molecular weight intractable tarry components ofaromatic hydrocarbon coolantmoderators into coolant types suitable foruse in a nuclear reactor.

A further object of the invention is to employ a catalytichydrogenolysis treatment for reconditioning polyphenylmoderator-coolants for use in a nuclear reactor.

Other objects and features of the invention will be come apparent byconsideration of the following detailed description.

The present invention contemplates the treatment of aromatic hydrocarbonmixtures employed as coolants and moderators or higher molecular weightfractions obtained therefrom by distillation, extraction, selectiveprecipitation, etc. The process is especially applicable to thetreatment of polyphenyl mixtures such as the damaged biphenyl-terphenylcoolant-moderator employed, e.g., in the OMRE and to other mixturesincluding, initially, biphenyl, terphenyls and quaterphenyls. Usuallysuch initial mixtures are fluid or have a low melting point and maycomprise a considerable proportion of biphenyl with terphenyl andquaterphenyls or eutectic mixtures. Alkylated biphenyl, terphenyls andminor amounts of quaterphenyls may likewise be employed. For thepurposes of the invention, a radiation damaged mixture is one that has ahigher average molecular Weight or undesirable amounts of high molecularcompounds and evidencing variously higher insoluble tar content, higherviscosity, melting point, etc. Certain polyphenyl synthesis methods mayproduce mixtures of too high a molecular weight which mixture maylikewise be treated. A damaged re actor or coolant material of thecharacter described may comprise discarded material, a bypass streamobtained from a reactor coolant system, residues obtained by selectiveseparation from a reactor coolant circuit, or the like.

In accordance with the invention such a material is subjected to ahydrogenolysis treatment wherein a substantial portion of the highermolecular weight components are converted into lower molecular weightcomponents such as biphenyl, terphenyl and alkylated derivatives thereofwhich constitute superior reactor coolantmoderator types. With sourcematerials not originally too severely damaged the reaction product,after filtering and being separated from gaseous or low-boilingcomponents, is reintroduced into the operating reactor as reconditionedmaterial. With highly damaged materials, such as the insoluble,intractable tarry residues the reaction product may be fractionated,e.g., in distillation or vacuum distillation apparatus and the recoveredlower molecular weight, components may be used as makeup xiimoderator-coolant or otherwise admixed with other compolyphenyls of ahigher molecular Weight than terphenyl, ponents to providemoderator-coolants as in conventional e.g., quaterphenyls, et seq., ageneral lowering of molecupractice. la-r weight will be obtained withsubstantial amounts of In the hydrogenolysis treatment the damagedcoolantbiphenyl and ter-phenyl being produced. Such mixtures moderatormixture is contacted with hydrogen in the would correspond or could beeasily blended to correpresence of a hydrogenolysis catalyst under highpresspond to the superior coolant-moderators disclosed in sure and atelevated temperatures in appropriate batch the aforesaid copendingapplication of Fontana et a1. or continuous flow high pressure equipmentof convenand publications supra. Hydrogenated polyphenyls tional design.Generally speaking, it is contemplated that which are produced underindicated conditions are less ,11 d id cracking d ild hydnogenationcatadesirable compounds since radiation damage resistance is lysts areeffective in producing hydrogenolysis of higher lower. polyphenyls. Morespecifically A1 0 (alumina) and Further details will be presented in thefollowing certain mixtures of A1 0 with CuO have been so em specificexample illustrating the manner of operating the ployed. Suitableoperating conditions are presented in process of the invention: Table I,infra. EXAMPLE TABLE I Standardized amounts of terphenyl representativeof higher molecular weight polyphenyls were reacted with Conditions Bmadrange Preferred range hydrogen under high pressure and at an elevatedtem- 0 perature with various combinations of cracking and hy-Timerhmns-flo -1 drogenation catalysts. The reagents comprisedMoniniil'd fi gs fiie,gjsiignwni E -8881 Same m-terphenyl recrystallizedfrom ethyl alcohol; Ram mpwnd: A1103 23 36 to aluminum oxide powder(Baker, reagent grade) as cracking catalyst; and copper oxide powder(Mallincrodt GP.) as hydrogenation catalyst. The reagents were chargedGeneral comments as to the effects of the specific into a hydrogenationbomb and the bomb pressurized secatalyst type are summarized in thefollowing chart: 'quentially to 500' and 250 p.s.i.g. with H toeliminate Chart Catalyst Effect on biphenyl formation Efieet on ringhydrogenation Efiect on higher polyphenyl formation Hydrogenation (OuO)Cracking (A1203) Increasing amounts decrease biphenyl rmation.Increasing amounts probably increase biphenyl formation.

Increasing amounts increase ring hydrogenation.

No ring hydrogenation obtained with cracking catalysts alone.

Increasing amounts probably reduce hgher polyphenyl formation.

Increasing amounts probably increase higher polyphenyl formation.

Norm-General comments: (1) Both ring-hydrogenation and hydrogenolysisreactions are strongly afiected by temperature and reaction time. (2) Itis likely that the catalyst for optimum operation (low conversions tohigher polyphenyls and hydrogenated polyphcnyls and high conversions tobiphenyl) will be primarily a cracking catalyst, with a small amount ofa mild hydrogenation catalyst.

Poly-phenyls can be represented by the formula wherein It may be zero ora larger integer, i.e., 1, 2, 3 Presumably, polyphenyl tars containsubstantial air and finally the desired hydrogen pressure wasintroduced. The bomb was then placed in a rocking hydro- 50 genationfurnace and heated to the desired temperature TABLE II Summary ofConditions for T erphenyl Hydrogenolysis Runs Conditions 6064- 6064-396064-42 6106445 6064-47 Time, hours 4 3. Temperature, F 800 900. Initialpressure, D.S.i.g 1,500 5G0 500 500 1,000. Terphenyl m-TerphenyL.m-Terphenyl o-TerphenyL- o-Terphenyl o-Terphenyl. Terphenyl charge, g. 225 5 50. Cat 1312090110-... AlzO3-C110 AlzOa-CuO. A1 0 A1203. Catalystcharge, g.:

CuO 1 0. Ratio of compound: AhOyCuO charges 25:420.

amounts of materials in which n is 2, 3 or larger while in desirablemoderator-coolants n is 0, 1 with at most minor amounts of quaterphenyls(11:2). The term hydrogenolysis as employed herein is intended to indi-Following hydrogenolysis the reaction products were removed from thebomb whereupon it was noted that the CuO in each instance was reduced tothe metallic state. Catalyst was separated from the mixture and themixture analyzed by means of a mass spectrograph with results presentedbelow in Table III:

TABLE III containing higher polyphenyls, the steps comprisingwithdrawing said damaged moderator-coolant from the Summary of MassSpectrometer Analysis of Terphenyl H ydrogenolysis Runsijiinieiiizi-Ec'e'tii'e this cene phenanthrene 230-.. 'Ierphenyl 234-Tetrahydro-terphenyl 236 Hexahydro-terphenyl 242.- Dodeeahydro-terphenyl"=0 Benzpyrene 306..-- Quaterphenyl 382 Quinquephenyl 458 Hexapnenyl535- Heptapnenyl 1 In calculating the components in 6064-35, certainassumptions concerning sensitivities had to be made. These assumptionsare listed on 6205-15.

Polyphenyl values for 6064-39, 42, and 45 are normalized to 100%. Thesepolyphenyls comprise approximately 96% of the total product for thesethree runs.

3 x denotes peak presence in small but undetermined amounts.

NOTE.-Figures in table refer to liquid volume percent concentration.

in practice the small proportions of polyphenyls above quaterphenylsshown would not seriously detract from the eflectiveness of the mixturesas coolant-moderators, particularly when the mixtures are employed formakeup. The lower boiling materials could, of course, be separated,e.g., as by distillation and employed as coolants and the higher boilingmaterial reprocessed.

While there has been described in the foregoing what may be consideredto be preferred embodiments of the invention, modification may be madetherein without departing from the spirit of the invention and it isintended to cover all such as fall within the scope of the appendedclaims.

What is claimed is:

1. In a process for producing a polyphenyl moderatorcoolant from amixture including higher polyphenyls, the steps comprising contacting anadmixture of said higher polyphenyl mixture and hydrogen simultaneouslywith a catalyst including an alumina acid cracking catalyst togetherwith a lesser proportion of CuO as a mild hydrogenation catalyst in theratio range of :2:1 to 25:4:(), respectively, at a temperature in therange of about 800 to 1000 F. and a pressure in the range of 500 to1,000 p.s.i.g. to cause hydrogenolysis of said higher polyphenyls toproduce lower molecular weight polyphenyls and alkylated derivativesthereof in the reaction mixture, and fractionating said lower molecularweight polyphenyls from said reaction mixture.

2. In a process for reconditioning a radiation damaged polyphenylnuclear reactor coolant-moderator mixture nuclear reactor, contacting anadmixture of said damaged reactor coolant-moderator and hydrogensimultaneously with a catalyst including an alumina acid crackingcatalyst and Q10 mild hydrogenation catalyst present in the ratio rangeof 25:2:1 to 25:4:0, respectively, at a temperature in the range ofabout 800 to 1000" F. and a pressure in the range of 500 to 1000p.s.i.g. to cause hydrogenolysis of said higher polyphenyls to producelower molecular Weight polyphenyls and alkylated derivatives thereof inthe reaction mixture, and then returning said coolantmoderator mixtureto the reactor.

3. The process as defined in claim 2 wherein there is included theoperation of fractionating said reaction mixture prior to return to saidreactor.

References Cited in the file of this patent UNITED STATES PATENTS2,033,878 Burk Mar. 10, 1936 2,297,769 Ipatieff et al. Oct. 6, 19422,344,258 Miles Mar. 14, 1944 2,355,219 Ipatieff et al. Aug. 8, 19442,364,719 Jenkins Dec. 12, 1944 2,800,518 Pitzer July 23, 1957 2,921,891Colichman Jan. 9, 1960 OTHER REFERENCES Atomic Energy CommissionDocument: ANL5121, Engineering Properties of Diphenyl, Anderson, Aug.11, 1953, pp- 14 and 15.

Catalysis, Sophia Berkman et al., pp. 629 and 847.

1. IN A PROCESS FOR PRODUCING A POLYPHENYL MODERATORCOOLANT FROM AMIXTURE INCLUDING HIGHER POLYPHENYLS, THE STEPS COMLPRISING CONTACTINGAN ADMIXTURE OF SAID HIGHER POLYPHENYL MIXTURE AND HYDROGENSIMULTANEOUSLY WITH A CATALYST INCLUDING AN ALUMINA ACID CRACKINGCATALYST TOGETHER WITH A LESS PROPORTION OF CUO AS A MILD HYDROGENATIONCATALYST IN THE RATIO RANGE OF 25:2:1 TO 25:4:0, RESEPCTIVELY, AT ATEMPERATURE IN THE RANGE OF ABOUT 800 TO 1000*F. AND A PRESSURE IN THERANGE OF 500 TO 1,000 P.S.I.G. TO CAUSE HYDROGENOLYSIS OF SAID HIGHERPOLYPHENYLS TO PRODUCE LOWER MOLECULAR WEIGHT POLYPHENYLS AND ALKYLATEDDERIVATIVES THEREOF IN THE REACTION MIXTURE, AND FRACTIONATING SAIDLOWER MOLECULAR WEIGHT POLYPHENYLS FROM SAID REACTION MIXTURE.